1. Field of the Invention
The present invention relates to the implantation of an intramedullary nail (IMN) for repair of long bone internal fractures. More specifically, the present invention relates to a system and method for targeting and placement of locking members in an IMN by means of magnetic and mechanical guidance. The present invention provides guidance for both proximal and distal targeting in an IMN.
2. Brief Description of the Related Art
In order to repair long bone fractures it is often necessary to use implants known as intramedullary nails (IMN). For example, an IMN can be used to repair an internal fracture of the femoral or tibial shafts. Advantages associated with the usage of an IMN include providing sufficient stability to maintain alignment and length, and limit rotation of the fracture site. Further advantages include minimally invasive techniques, reduced hospitalization, earlier postoperative ambulation, and earlier active range of motion (ROM) when compared to some conventional casting or external fixation methods.
The standard operating procedure for the fixation of long bone fractures with an IMN consists of the implantation of the IMN, an elongated, rod-like, metallic orthopedic appliance into the affected medullary canal of a given long bone. The clinician typically starts with an incision and thereafter creates an opening in the proximal or distal end (antegrade or retrograde) of a given long bone, thereby providing access to the affected medullary canal in which the IMN is then implanted. One goal in IMN treatment is fracture reduction so that near anatomic alignment takes place under stabilized conditions, often facilitated by means of locking members, for example, locking screws that are integrated with an IMN.
A given IMN is prefabricated, for example, with locking holes that are located in the general vicinity of the proximal and distal ends of the IMN. These locking holes can accept one or more interlocking screws. The locking screws when interlocked with an IMN are designed to stabilize the fracture and fix the bone relative to the implanted IMN.
Proximal interlocking screws are relatively easy to place in their corresponding locking holes due in part to minimal deformation at the proximal end of an implanted IMN and the use of rigid targeting guides that are fixed to the proximal end of the selected IMN. These external proximal targeting guides have integral guide bores oriented and positioned inline with the effective central axis of the proximal locking holes, thus facilitating proximal locking. In contrast, one of the most difficult procedural aspects of implanting an IMN has been the location, alignment, drilling and subsequent placement of the distal locking screws. This difficulty stems in part from distal deformations that occur in some IMN's when they are implanted in the affected medullary canal.
At least one contemporary study has demonstrated that a larger-diameter IMN, (cannular 13-mm) can, upon implantation, exhibit lateral deformations of 21.5±7.9 mm (range: 26.4 mm), dorsal deformations of 0.4±9.8 mm (range: 30.1 mm), and rotational deformations about the longitudinal axes of 10.0±3.1 degrees (range: 7.8 degrees). Such IMN distal end deformations make it difficult to use and rely on conventional targeting guides. Also, tight manufacturing tolerances that are needed between the IMN and the interlocking screws adding to the difficulty.
Attempts have been made to compensate for the above-mentioned deformations, through the use of hand-held powered magnetic targeting systems. Such techniques can include the use of a probe inserted into a cannular IMN. Once the probe in such a system is in place near the desired IMN's distal locking hole position, a hand-held guide is used to maintain proper alignment of a drill, and an electromagnetic display unit connected to the probe displays visual images that graphically indicate the manner in which the guide must be moved to bring it into proper alignment. Unfortunately, to ensure the drill hole is actually made in the desired location, such a system must still rely on the steady hand of the orthopedic surgeon, intense eye-hand coordination and is subject to the inaccuracies related to drill walk.
Unfortunately, contemporary apparatus fail to solve the problem of effectively targeting the distal locking hole positions. The combination of the deformation of the implanted IMN, the slight shake that is natural in hand-held instruments, the drift that often occurs with contemporary drills when drilling through bone, and other factors make it difficult to actually drill a hole that properly aligns with a distal locking hole position. Also, contemporary devices do not provide a reliable overall system for targeting and securing both proximal and distal locking hole positions.